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70th Birthday of
Professor D. K. Ross


Professor Keith Ross was born in Ballymoney, Co Antrim in Northern Ireland on 16th July 1939, just before the outbreak of the Second World War. His early interest in science was stimulated by the fact that his father, then the headmaster of the local grammar school (Dalriada), was a physical chemist who had gained his PhD at University College London, where he built an early Infra Red spectrometer and who had subsequently worked for ICI on the development of commercial sulphuric acid production prior to turning to school teaching.
Having attended Dalriada, Portadown College and Campbell College in Belfast, he gained an open exhibition to Pembroke College, Cambridge where he read Natural Sciences. On graduating, he did an MSc in Reactor Physics and Technology in Birmingham University and then went to work for the UK Atomic Energy Authority at Winfrith Heath in Dorset. Here he worked on experimental sub-critical nuclear assemblies, developing neutron chopper techniques for measuring the internal neutron spectra. After three years at Winfrith, he was invited back to Birmingham by Professor John Walker to apply his knowledge of neutron physics in the newly emerging field of neutron scattering. The original objective of this work was to measure the inelastic scattering cross sections of potential reactor moderators – information required to model the neutronics of power reactors. This programme involved the construction of a neutron chopper facility at the Herald Reactor at AWRE (now AWE), Aldermaston. This was 5 Mwt light water/enriched uranium reactor equipped with an H2/D2 cold source. With his early research students, he was able to build his own novel neutron scattering instruments. Starting from a beryllium filter, cold neutron chopper, time-of flight spectrometer, they subsequently built a fast neutron chopper/beryllium detector spectrometer, a rotating crystal spectrometer and double graphite monochromator chopper spectrometer. The first experiments were on high pressure water at temperatures up to 250oC and on graphite up to 2000oC. Once the data requirements for reactor moderators had been satisfied, he was able to apply the neutron scattering technique to a variety of condensed matter problems. His early students at AWRE included Colin Carlile, subsequently Director of the Institute Laue Langevin, Grenoble and Ian Anderson, currently Director for Neutron Sciences at Oak Ridge National Laboratory in the USA who also used their experience in designing and building neutron scattering instruments on Herald in their subsequent careers. He obtained his PhD in 1975 on some of this work. In 1973, the UK joined the ILL and from then until the operation of ISIS at the Rutherford Appleton Laboratory in 1985, his research was centred on the ILL. Thereafter, he has used both these world-leading sources as appropriate for different experiments. In the area of hydrogen in metals has since this time D.K. Ross had a continuing collaboration with Prof. Rex Harris in Birmingham. He obtained a DSc in 1985 and was appointed to a Readership in Birmingham in 1989. In 1991, he moved to the University of Salford to take up the established chair in Physics. Here he was at different times the Head of the Physics Department and Director of the Institute for Materials Research and is currently the Director for the Centre in Functional Materials. He has currently authored about 180 refereed journal articles with an h-index of 27 and is currently leading four significant research projects.
Because of hydrogen’s anomalously large neutron cross section, it was obvious to apply neutrons to the study of its behaviour in solids. An early interest was in the use of quasi-elastic neutron scattering to investigate the diffusion of hydrogen in palladium, analysing the observed broadening using the Chudley-Elliott model. The extension of this method to cover different situations became a theme of his career. Having demonstrated that in the α-phase of palladium, hydrogen diffuses as a lattice gas by jumping between nearest neighbour octahedral sites (Carlile and Ross 1974), he demonstrated theoretically how correlation effects influence the shape of the quasi-elastic scattering, both in the incoherent and coherent scattering cases (Ross and Wilson 1977). He also applied the technique to the case of water diffusing between alumino-silicate layers in clays, here developing theories to describe quasi-elastic scattering from atoms diffusing between fixed boundaries (Hall and Ross, 1978,1981) and these theories have since been widely used to analyse this type of experiment. Another extension of the theory dealt with coherent quasi-elastic diffusion where the diffusing atoms interact with each other, culminating in the publication of a density response function treatment with Sinha (1988). With Cook and others (1990), he used the technique of neutron spin analysis to separate the coherent and incoherent quasi-elastic scattering from Nb-D, demonstrating directly the process of “critical slowing down”. One interesting aspect of an interacting lattice gas is how it behaves on cooling down. With Bond (1982), he developed the use of Monte Carlo simulations to investigate the ordered structures that appear in f.c.c. lattice gases on cooling. This approach explains the well known 50K anomaly in the Pd- H(D) system where a superlattice with the symmetry I41/amd is formed showing a superlattice reflection at (1,1/2,0) (Anderson, Ross, Carlile, 1976,1978). The ordering process is second order and occurs at a rate conveniently studied with neutrons. With McKergow and others, D.K. Ross observed the transition between short and long range order in this system and formulated the process by which the tetragonal distortion of the ordered compound generates tensile stresses that in turn limit its growth. A similar situation applies in the α- phase of a number of rare earth hydrides particularly yttrium which show complex short range ordering (with McKergow, Anderson and others 1987). The Monte Carlo approach was also applied to Fick’s Law Diffusion and coherent quasi-elastic scattering (with Faux, 1987 and Bull, 2001) and to the similar problem in NMR (with Faux and Scholl, 1986).
Inelastic neutron scattering is also well suited to the study of hydrogen in metals because in many systems, the hydrogen vibrates as in a simple harmonic oscillator. The resulting peak in the inelastic scattering was measured in many systems. With Oates and others (1979), he showed that the peak energy for tetrahedral site occupation (fluorite structure) varies as R-3/2 where R is the hydrogen-metal distance and, with Fernandez and others (1999), he showed how the vibration frequencies observed in Laves Phase hydrides could be related to the metallic constituents. More recently the techniques of density functional theory have advanced to the point where rather precise predictions of the proton quantum states, and hence of the inelastic scattering are possible from first principles. With Totolici, Kemali and Morrison (2000), he demonstrated that the measured scattering from a single crystal of PdH very closely matched the calculations up to the third excited state with no arbitrary parameters. With Li, inelastic neutron scattering has also been applied to the study of the vibrations of various ice systems, where the complication exists due to the large number of different phases and the fact that in the proton disordered phases, the proton arrangement is described by the Ice Rules. A simple rationalisation of this complexity in terms of weak and strong force constants (Nature 1993) continues to be a source of controversy. With Li and Benham (1989, 1994) he also adapted the Small Angle Neutron Scattering/contrast matching technique to study how the pores in Vycor lose a liquid phase as the external partial pressure is reduced, a method that has proved to be a powerful way of understanding the interconnection of pores in solids.
In recent years his main interest has been in the use of neutron scattering to study the behaviour of hydrogen in potential hydrogen storage systems. In a series of papers with Georgiev and others, he observed the scattering from para-hydrogen adsorbed on surfaces. Here the scattering is dominated by the transition between the molecular rotational states l = 0 (para) to l = 1 (ortho) at 14.7 meV. When the molecules are trapped in a potential well, the substates of the l = 1 become split and the nature of the splitting provides direct information on the trapping potential. The technique has been used on a number of potential molecular hydrogen stores (nanotubes, activated carbon and zeolites) and has indicated the possible ways of increasing the interaction potential, crucial to producing a viable hydrogen store.
Professor Keith Ross has played a significant role in the development of the subjects he is interested in, giving a considerable number of invited lectures. He is currently Secretary of the International Steering Committee of the International Symposia on Hydrogen-Metal systems.

Dr Zh.A. Mileeva
August 2009